Conventionally, urethane foam is used, for example, in the seats 81 and 82 of an automobile 80 illustrated in FIG. 8. Automobile seats 81 and 82 are classified into front seats 81 and rear seats 82. As illustrated in FIG. 9, each of seats 81 and 82 consists of a cushioned part 83 which supports one's buttocks directly, and a backrest 84 against which one's back is leaned. Roughly speaking, each seat is made up of four components as illustrated in FIG. 9. They include a frame 83a or 84a providing the framework of the seat, springs 83b or 84b for maintaining cushioning properties, urethane 83c or 84c serving to absorb vibrations, and a skin 83d or 84d protecting the urethane and coming into direct contact with one's body. Among such urethanes 83c and 84c, especially the urethane 84c constituting the backrests is required to have softness and holding properties.
A lightweight cold urethane is especially suitable for use as the urethane constituting the backrests (i.e., back urethane).
However, conventional lightweight cold urethanes had the following problems.
(1) Conventional lightweight cold urethanes have a density of about 40 kg/m3 and are heavier than hot urethanes (27-35 kg/m3). They require a larger number of raw materials to be injected into a mold, and hence involve a high cost. Moreover, they cause a corresponding increase in car body weight and hence bring about poor fuel consumption.
(2) In conventional formulations, the density can be reduced to some extent (34 kg/m3) by increasing the amount of water (i.e., the number of parts of water). However, this causes a problem in that the resulting urethane no longer has flame retardancy. Although the addition of a flame retardant is conceivable, this causes an increase in cost and is hence impractical. Moreover, the resulting urethane gives an easily yielding pad and fails to meet performance requirements for seats.
As a lightweight cold urethane solving these problems and meeting property requirements such as excellent flame retardancy, the present inventors developed a lightweight cold urethane as disclosed in Japanese Patent Provisional Publication No. 10-176025. However, this lightweight cold urethane still has an unsolved problem in that the type of polyol used is limited.
Accordingly, there is a need for the preparation of a lightweight cold urethane having a flame-retardant formulation using common polyols. Additional urethane formulations are described in Japanese Patent Provisional Publication Nos. 5-320304, 6-166042 and 5-202164. However, none of them can bring about an improvement in flame retardancy.
On the other hand, it has been conventional practice to feed two urethane-forming raw material fluids from raw material fluid sources into an injection head through separate hoses, and inject them from the injection head into a lower mold section. Both fluids are mixed by collision in the injection head and then injected into the mold. Moreover, such a two-component foaming mold has been developed so as to use a four-component injection head. This permits various types of urethane foam having different densities and hardnesses to be formed with a single injection head.
When such an injection head is used, it is preferable that, among various compounding ingredients, auxiliary ingredients be mixed and placed in one working tank. However, in conventional formulations, this auxiliary ingredient mixture consists chiefly of water. This has been problematic in that the piping is apt to rust and a homogeneous fluid cannot be formed because of the poor miscibility of water and an oily silicone foam stabilizer or the like. For this reason, even the use of a four-component injection head has been unable to produce satisfactory results.